The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A conventional wood gasification apparatus uses only the friction created by a fixed screw and barrel. The screw design is typically one of a continuous decreasing volumetric design which increases the pressure on the cellulosic material and maximizes the frictional heating until the material reaches a temperature above its autoignition temperature. Once the vaporization temperature is reached, the cellulosic material is converted into a combination of combustible fuel gases that typically contains a mixture of methane, hydrogen and carbon monoxide. Any particulate material that is present is frictionally heated and propelled along the auger until it reaches a plasticizing or softening temperature and forms an in-situ seal between the auger and the housing. This in-situ seal prevents gas from flowing back along the auger to the housing inlet.
However, in practice, a conventional wood gasification apparatus is also prone to plugging as the plasticized is carburized. This plugging can be catastrophic, shutting down the process by overloading the electrical current and/or shearing coupling drives and/or bolts. Additionally, the plasticizing seal is minimal to non-existent when processing non-woody biomass due to lower lignin content. Once a plug forms, the unit must be allowed to off-gas, cool to below the autoignition temperature and then be disassembled for cleaning. The carbonized mass must be scraped from the threads and inside of the housing, a process that takes hours, which results in substantial lost production time.
A rotary compression unit (RCU), often referred to as a rotary biomass dryer, provides a low cost alternative to conventional biomass drying and processing. The RCU requires no external energy, only a motor to rotate the compression auger effectively heating the biomass by compression and friction to generate in-situ steam.
The RCU, which often has an adjustable nozzle, is also equipped with a compression screw. Similar to the wood gasification apparatus, the rotary biomass dryer is prone to plugging, which results in hours, if not days, to clean and restart the process. For RCU's powered by 100-500 horsepower, plugging may occur without notice and require a large hydraulic jack to extract the screw. In addition, the biomass dryer is deployed with an adjustable nozzle that is cumbersome and prone to high wear. During processing, only the biomass in direct contact with the compression screw or elongated tube is dried during the process.